Samples of solid materials, and particularly road and paving materials such as bituminous mixtures and aggregates, are commonly subjected to standardized tests to determine certain properties such as specific gravity. For example, ASTM International has published the following standards, the contents of which are incorporated herein: ASTM D 2041—95, entitled “Standard Test Method for Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures” (also known and referred to hereinafter as “the Rice test”); and ASTM C 128—97, entitled “Standard Test Method for Specific Gravity and Absorption of Fine Aggregate” (hereinafter “the fine aggregate test”). Results from such tests are used both for the purpose of design and quality control.
The Rice test is employed to determine the theoretical maximum specific gravity and density of uncompacted bituminous paving mixtures at 25° C. Prior to subjecting the sample paving material to the Rice test, the sample must be prepared so as to be uncompacted, meaning that the sample must be brought to a loose, cool state. The conventional preparation method requires that a technician manually separate the particles of the sample so that the particles of the fine aggregate portion are no larger than 6.3 mm (¼ inch) each. This preparation process is labor intensive and time consuming, as it involves heating a sample to 100+/−° C. in an oven, and stirring the heated sample in a flat pan for twenty minutes or more while the pan is positioned in front of a fan.
The fine aggregate test is employed to determine bulk specific gravity (for example, the percentage of voids in a mineral aggregate) and absorption (for example, the amount of asphalt binder absorbed by the aggregate) on the basis of the weight of a sample aggregate that has reached a saturated-surface-dry (SSD) condition after being immersed in water for twenty-four hours. Thus, preparation of an aggregate sample for the fine aggregate test requires drying the sample to the SSD state. The conventional dry back method for fine aggregate, as described in ASTM C128-97, is performed manually or with the use of a mechanical tumbler, and the sample is frequently tested for SSD condition using one of three methods described therein. Typically, this process takes at least two hours and, accordingly, like the preparation required for the Rice test, is labor intensive and time consuming.
It would therefore be advantageous to provide an automated apparatus adapted to perform a sample preparation process, whether in preparation for the Rice test, the fine aggregate test, other tests, or for mixing. Such an automated apparatus would significantly reduce the expenditure of time and labor conventionally involved in material sample preparation, thereby allowing the technician to perform other tasks while the sample is being prepared by the apparatus. In addition, particularly in the case of fine aggregates, a need is recognized for developing more accurate and reproducible test methods. See, e.g., Kandhal et al., “Measuring Bulk-Specific Gravity of Fine Aggregates,” Transportation Research Record 1721, Paper No. 00-1230, p. 81 (2000). The need for improved accuracy and reproducibility can be addressed by the use of an automated apparatus, since the automation would reduce the degree of subjectivity and manual effort involved in the sample preparation.
Kandhal et al. have proposed an automated technique for preparing a fine aggregate sample for the testing of bulk specific gravity. Their technique involves placing a wet sample of fine aggregate in a rotating drum and subjecting the sample to a steady flow of warm air. The temperature gradient of the incoming and outgoing air and the relative humidity of the outgoing air are monitored to establish the SSD condition. The drum was equipped with screens to confine the sample in the drum. However, it has been found that a drum such as that proposed by Kandhal et al. allows an unacceptable amount of sample to be lost through the inlet and outlet of the drum. This material loss is a consequence of the air flowing through the drum carrying away sample particles as the sample is being dried and/or cooled, as well as a result of the rotation of the drum and comcomitant agitation and movement of the sample. It would therefore also be advantageous to provide an automated apparatus adapted to perform a sample preparation process while preventing or at least reducing the amount of material loss unrelated to drying of the sample.